Coast Resorts Open Roads Forum: Towing: Breakaway Switch - Before the fuse?
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 > Breakaway Switch - Before the fuse?

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Posted: 04/17/14 09:33am Link  |  Quote  |  Print  |  Notify Moderator

I recently had some work done on the trailer and the breakaway switch was connected to the blue brake wire on one side and ground on the other. That "ground" connection needs to be moved....

It looks like the breakaway was originally connected to a 60Amp (assuming because converter is 55A....) fuse lug and I *think* it was connected on the battery side of the fuse. Is that typical?

I suspect that connecting to the fused side just introduces another failure point (the fuse). Since the breakaway wires are so small, they would melt before tripping the fuse anyway.....

I've connected the breakaway to the battery side lug (unfused) for now. Is there a good reason to connect it to the fused side?


King George, VA

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Posted: 04/17/14 11:00am Link  |  Quote  |  Print  |  Notify Moderator

Each BRAKE MAGNET draws 3AMPs EACH with 12VDC applied. Two wheels is 6AMPS - Four wheels is 12AMPS... When your break-away switch is activated it will provide a full 12VDC from your TRAILER BATTERY to all of the connected BRAKE MAGNETS.

Looking at two or three installation guides online including ETRAILER.COM I didn't see where a FUSE was installed in-line. However the battery is capable of alot of power being developed during a short circuit. A couple hundred AMPS probably - maybe more. A short circuit will definitely melt your break-away switch wiring and we have seen that reported on here... A wiring catastrophe fuse would eliminate this from happening. I don't think my wiring has any in-line fuse involved.

Probably your call whether or not you want one installed.

Roy Ken

* This post was last edited 04/17/14 11:21am by RoyB *   View edit history

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Posted: 04/17/14 11:40am Link  |  Quote  |  Print  |  Notify Moderator

I did a little test. Do these breakaway switches have a resistor or something to reduce voltage?

When I use my controller lever and apply full brakes I can hear the magnets hum.

If I pull the breakaway switch, I cannot hear the magnets hum.

With the breakaway switch pulled, I can see that about 12A of current is drawn from the batteries and I can measure about 1.5 volts across the two breakaway wires.


La Quinta, CA

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Posted: 04/17/14 12:02pm Link  |  Quote  |  Print  |  Notify Moderator

With two axles (4 brakes) my toyhauler has a 30 amp circuit breaker in line with the circuit feeding back to the brakes from the trailer hitch area and another in line with the power from the house battery to the breakaway switch. Since it's assumed that the trailer plug will detach from the TV if the hitch disconnects, the breakaway should be connected to the house battery, so the brakes can work even if unplugged from the TV. As I already said, mine are protected by the 30 amp breakers, so I would imagine that the point of using a breaker instead of a fuse is that it automatically resets after cooling and can allow power to flow again to the brakes after it resets.

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Verde Valley

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Posted: 04/17/14 12:55pm Link  |  Quote  |  Print  |  Notify Moderator

Breakaway switch allows FULL trailer battery voltage to be applied to trailer brake magnets should the 'pin' get pulled out.

12V DC power directly from trailer battery to switch to trailer brakes.
Power in and power out of switch.
Both wires on switch are 12V DC 'positive'.......not connected to ground

The switch is just that.......a switch. Contacts make up when pin is pulled allowing 12V DC current to flow.


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Posted: 04/18/14 03:37pm Link  |  Quote  |  Print  |  Notify Moderator

I'm not sure where the voltage drop across the breakaway is coming from. I can see that about 12A of current is being pulled from the battery so it **appears** as if the breakaway is operating properly.

In checking all this out I discovered that every single visible ring terminal crimp is loose - some worse than others. My guess is that the closed end ones are bad as well.

I also discovered that the brake wires are 14G. According to the axle manufacturer, this is too small for a 35' trailer. Now I'm on a quest to to fix that.


Radnor, Ohio, USA

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Posted: 04/18/14 07:55pm Link  |  Quote  |  Print  |  Notify Moderator

From what I have seen and go by, the breakaway is to be hot all the time to the camper battery. If you have a battery disconnect, it goes on the upstream side of the switch so you always have the emerg back up power available.

As to a fuse for short protection, mine does not have any on the breakaway. That said, if you want one, I would go with a self resetting circuit breaker over the fuse. I would pick a 30 amp, I have no 10# awg brake wire except for the break away. A dead short should trip it fast enough before total melt down. In my case the , #14 gage wire on the breakaway switch becomes the fuse.

To your question on a resistor in the break away switch, I have not found there is one in the switch. However the setup can create a voltage drop. Most have 6 feet of total wire length, 3 ft to and 3ft from, the switch. That #14awg may be your voltage drop point. And the switch itself may have some resistance drop. I noticed the same thing on my sons PU. While it is live hot to the battery, that does not mean you will deliver full current to the brake coils. Poor trailer wiring and then the smaller gage wire at the switch does not help the cause.

Hope this helps


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